It has been generally known to make hemodialyzers by utilizing hollow membrane filter elements supported axially within a cylindrical housing. Such housings usually have fluid flow input port and an output port. Fluid injected into the input port flows through the hollow membrane filter elements. The housings also include dialysate input and output ports. The dialysate flows around the exterior surfaces of the hollow membrane filter elements.
The filter elements can be formed from a variety of natural as well as synthetic materials. For example, hollow membrane fibers can be formed of polysulfone, polyethylene, cellulose or cuprammonium. A common form of cuprammonium is available from Enka under the trade name CUPROPHAN. It is also known that use of these differing materials results in dialyzers with substantially different characteristics. Dialyzers of polysulfone and polyethylene are known to be more biocompatible then dialyzers of cuprammonium. On the other hand, polysulfone dialyzers are more expensive than cuprammonium dialyzes. Also, cuprammonium dialyzers have better ultrafiltration performance characteristics than do polysulfone dialyzers.
Whatever the selected hollow fiber material or size, it is necessary to encase the appropriate numbers of fibers in a housing. In the past, dialyzers have been manufactured by arriving at a particular number of fibers, of certain type and size. These fibers can then be encased to provide a dialyzer with the appropriate ultrafiltration perameter.
Casings or housings can be injection or blow molded. A particular housing can be used with only a few different selected number and type of ultrafiltration fibers. In part, this is due to the internal crossection of the housing. In addition, space must be provided around the fibers so that the dialysate can freely flow around same to effect filtration.
Hence, if the number, type, or size of the ultrafiltration fibers is to be altered due to a desire to change the ultrafiltration perameter, or any other characteristic of the dialyzer it may be necessary to create molds to make a new case. This is a very expensive process.
It would be desirable to be able to vary the contents of a hemodialyzer in order to alter the dialyzer parameters while continuing to use existing housings. For example, combining polysulfone with cuprammonium might result in a lower cost dialyzer, than a completely polysulfone dialyzer. Such a dialyzer could still be adequately biocompatible but with greater ultrafiltration performance characteristics than would be the case of a dialyzer having only polysufone fibers. Cuprammonium could also be combined with cellulose acetate or polyethylene. Similarly, it would be desirable to blend fibers of the same type having different radii. However, the prior art does not disclose how to carryout such blending and still use an existing housing. Hence, there is a need for a method of making hemodialyzers which is substantially more flexible and less expensive then known methods.